High Quality Content by WIKIPEDIA articles! Custer County is a rural mountain county located in the center of the U.S. state of Idaho. Established in 1881, it was named for the General Custer Mine, where gold was discovered five years earlier (shortly after his death at the Battle of the Little Bighorn in eastern Montana). The population was 4,342 at the 2000 census; it is estimated to have fallen to 4,166 by 2007. The county seat is Challis. The center of population of Idaho is located in Custer County, in the city of Stanley.